Prostate cancer is the most common cancer diagnosis and the second leading cause of cancer- related death in American men. Standard anti-cancer drugs often fail to control localized prostate cancer, suggesting that new targets and new treatment approaches are needed. After the recent discovery of tumor-initiating cells (or cancer stem cells, CSCs) in all major human cancer types, including prostate cancer, accumulated data revealed that not any cancer cell, but only the pathological pool of CSCs are responsible for tumor initiation, development, invasion and response to treatment in the majority of human cancers. Therefore, CSCs are likely to be the most crucial target for cancer treatment. In our previous studies we have identified and characterized several phenotypic subpopulations of stem-like cells, and obtained their genome-wide and pathway-specific characteristics. We have found that prostate cancer cells with the highest expression of CD133 and CD44 possessed high tumor-initiating and sphere-forming capacities, over-activation of several stem cell-related pathways, and up-regulation of many genes involved in the regulation of stem cell self- renewal, pluripotency, anti-apoptosis and drug resistance. We have determined that several new- generation taxoids not only induced significant cell death and growth inhibition in highly aggressive prostate cancer cells grown as 3D CSC-enriched spheroids, but also significantly altered their stemness state, decreasing an expression of several essential markers of pluripotency, including c- Myc, Oct4 and Sox-2, and a large spectrum of other stem cell-related genes. The main hypothesis of this proposal is that selected new-generation taxoids will be effective against prostate CSCs isolated from a broad spectrum of clinical specimens. One of our goals is to develop and standardize a technically straightforward in vitro prostate CSC model for the evaluation of the CSC-targeted drug effects. We will determine the cellular and genomic alterations induced by new-generation taxoids against functionally significant prostate cancer cells, CSCs, not just bulk tumor cells, under stringent, clinically relevant conditions. We will employ new criteria for evaluation of drug effectiveness, including long-term follow-up, and thorough analysis of the residual tumor tissues and cancer spheroids for the presence of the tumor-driving SCSs. In addition, we will create a bank of characterized prostate CSCs, which will be available to the research community. As a result of this project, a potential novel drug against currently incurable androgen-independent prostate cancer can be identified.